An orthogonal frequency division multiplexing technology (OFDM) is a system key multiple access technology of beyond third generation (B3G)/the fourth generation (4G) mobile communications systems, and is also a downlink multiple access technology used by Long Term Evolution (LTE)/LTE Advanced (LTE-A) systems.
In terms of time, a length of an OFDM radio frame is 10 ms, including 10 subframes. A length of each subframe is 1 ms, each subframe includes two timeslots, and each timeslot includes seven or six OFDM symbols. In terms of frequency, one OFDM radio frame includes multiple subcarriers. A subcarrier in an OFDM symbol is referred to as a resource element (RE), four REs form a resource element group (REG), nine REGs form a control channel element (CCE), and 12 subcarriers and one timeslot form a resource block (RB). RBs are classified into physical resource blocks (PRB) and virtual resource blocks (VRB); a PRB refers to an actual frequency location of an RB, and PRBs are numbered in ascending order; two PRBs form a PRB pair; a numbering form different from that for PRBs is used for VRBs, to map VRBs to PRBs by using a specific resource allocation manner. Various control information, reference signals or service data is transmitted on these time frequency resources.
A physical downlink control channel (PDCCH) is a channel that is defined in LTE Release-8/Release-9/Release-10. The PDCCH bears downlink control information (DCI). The DCI includes scheduling information, power control information, and the like, of a downlink data channel or an uplink data channel. In the prior art, an evolved Node B (eNB) may determine a search space of the PDCCH according to an aggregation level, and an user equipment (UE) obtains, by searching, an effective PDCCH in the determined search space. The PDCCH has four aggregation levels, which are 1, 2, 4, and 8 respectively, and indicates respectively that the PDCCH is mapped to one, two, four, and eight CCEs. One aggregation level corresponds to a search space size and the number of PDCCH candidates, that is, a possible PDCCH location that one PDCCH may be mapped to.
An enhanced physical downlink control channel (EPDCCH) is further introduced to LTE Release-11. The EPDCCH occupies physical resources of a data channel, and is multiplexed with the data channel in a frequency division multiplexing manner. The number of resources that are occupied by an EPDCCH is notified to a UE by higher layer or physical layer signaling. The eNB allocates one or more groups of time frequency resources for EPDCCHs in a search space, where one group of physical resources is referred to as an EPDCCH set. An aggregation level of an EPDCCH determines the number of enhanced control channel elements (eCCE) that are occupied by the EPDCCH. Transmission solutions of EPDCCHs may be classified into localized transmission and distributed transmission according to whether resources used by the EPDCCHs are continuous in the frequency domain. The search space determining manner in the prior art causes that multiple EPDCCH sets or UEs use a same search space, which leads to, when the number of users increases, a serious control channel congestion phenomenon and an obvious search space conflict phenomenon.